PSN-L Email List Message

Subject: slinky seismometer follow up
From: Kasper VanWijk kaspervanwijk@..............
Date: Wed, 16 May 2012 21:58:35 -0600

Dear PSN-ers:

After being forwarded a message from your user list and some other
e-chatter I picked up, I signed up to comment on a recent discussion
about the slinky seismometer. Let me introduce myself first: my name
is Kasper van Wijk, and I teach geophysics at Boise State University.
Shortly after moving to Boise, Mr. Ted Channel, a devoted psn-er,
contacted me about collaborating on home-built seismometers. Since
then, we (but mostly he) successfully built lehman's and developed a
short-period vertical sensor as simple as a magnet on a slinky in a
clear tube. In the early days, we relied a lot on Mr. Larry Cochrane
support: thank you, Larry!

We have fine-tuned the latter design in our latest version (VIII), as
we recognized it has some properties that make this an optimal unit
for schools; our primary target. Our sensors
pick up any EQ magnitude 6 or greater, worldwide. A good spot for the
sensor gets this actually down to about Ms 5.6. Clear P-wave arrivals
can be used for triangulation to the rough source position, and for
any other seismology exercise a K12 school.

After years of testing (among things, next to an AS1), I can
confidently state the device is not under-damped by any definition, as
long as the top of the magnets are flush with the top of the coil and
damper ring, respectively. (Besides, this was not what Doug is having
trouble with, as I understand it.) I just wanted to clear this up,
before this goes widespread among the experts at the psn! The second
point, however, about the sensor's frequency response is more
interesting: we have decided to produce an interface between sensor
and computer that is more or less flat in response (designed by the
father of one of Doug's colleagues: dr. martin smith). The result is
that our seismometer, just as the AS1, is largely a ~1s period
body-wave sensor, but I'll gladly post images showing (weak but
significant) evidence of surface waves. So it is true that we can
"boost" the low end of the recorded spectrum, to enhance longer-period
surface waves. We just have not done this (yet), but our interface is
based on the arduino uno ( The code to run it, is
freeware, and thus anybody is free to download the code via our
website and adjust as he/she sees fit.

We linked Martin's google project site for the NERdaq (the interface)
and tried to summarize a lot of information including how to build and
set up your slinky seismometer at,
but feel free to contact me at kaspervanwijk@.............. if you
have particular questions/comments. The page also has links to a few
of the many slinky seismometers recording earthquakes every day.

Doug, the spikes in your data are likely from a clock, possibly the
one in your computer, or one on the wall above the sensor.


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